Heretofore, lighting devices for performing light modulation control for light emission on a semiconductor light-emitting element have been provided (refer to Document 1: JP 2012-226924 A). A lighting device described in Document 1 includes a step-up chopper circuit and a step-down chopper circuit. The step-up chopper circuit is configured to rectify and smooth an AC power supply voltage, and output a constant DC voltage. The step-down chopper circuit is configured to step down an output of the step-up chopper circuit and supply the stepped down voltage to a semiconductor light-emitting element.
In the lighting device described in Document 1, light modulation control for light emission is performed on the semiconductor light-emitting element by the light modulation control circuit controlling an on-time width of a switching element included in the step-down chopper circuit.
Also, a lighting device is provided that is configured to perform light modulation control for light emission on a semiconductor light-emitting element by intermittently supplying a DC voltage that is outputted from a DC power supply according to a PWM signal. The lighting device includes a switching element that is electrically connected between the DC power supply and the semiconductor light-emitting element. The DC power supply is configured to output a DC voltage having a voltage value corresponding to the semiconductor light-emitting element.
In the lighting device, a square wave voltage according to the PWM signal is supplied to the semiconductor light-emitting element by turning on and off the switching element according to the PWM signal, and as a result, light modulation control for light emission is performed on the semiconductor light-emitting element.
Incidentally, in the latter lighting device described above, a current that is supplied to the semiconductor light-emitting element via the switching element includes harmonic components in addition to a fundamental wave component, and therefore light that is emitted from the semiconductor light-emitting element includes harmonic components as well.
Therefore, in the case where a barcode reader that emits light having the same frequency as a frequency of one of the harmonic components is used under lighting by the semiconductor light-emitting element when a barcode is read, for example, it is possible that the content of the barcode cannot be read due to light that is emitted from the semiconductor light-emitting element.